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Parasitology Review Test #2

***Reminder: Slides and examination questions are copyrighted and cannot be copied for publication.
  1. If amebic trophozoites measuring 13 µm and containing red blood cells within the cytoplasm are seen in a permanent stained smear, the correct report would indicate the presence of:
    1. Entamoeba coli trophozoites
    2. Entamoeba hartmanni trophozoites
    3. Entamoeba histolytica trophozoites
    4. Entamoeba polecki trophozoites

    ANSWER: The amebic trophozoites described above would be identified as Entamoeba histolytica (the presence of ingested RBCs allows this identification to be made). If no RBCs are seen in the cytoplasm of the trophozoites, the correct report would be: Entamoeba histolytica/E. dispar trophozoites seen. The correct answer is C.

  2. Intestinal protozoa that do not have a cyst stage in the life cycle include the following:
    1. Entamoeba hartmanni
    2. Iodamoeba bütschlii
    3. Pentatrichomonas hominis
    4. Dientamoeba fragilis

    ANSWER: Of the organisms listed above, the one that does not have a cyst stage in the life cycle is:  Pentatrichomonas hominis. The correct answer is c.

  3. An amebic cyst measuring 9 µm and containing four nuclei and chromatoidal bars with smooth, rounded ends is most likely:
    1. Endolimax nana
    2. Entamoeba hartmanni
    3. Iodamoeba bütschlii
    4. Entamoeba histolytica

    ANSWER: The amebic cyst described above would be identified as Entamoeba hartmanni (size and chromatoidal bars with smooth, rounded ends). The correct answer is B.

  4. If a patient has watery diarrhea, the stage in the life cycle of the intestinal protozoa that is most likely to be seen in the permanent stained smear is the:
    1. Cyst
    2. Precyst
    3. Trophozoite
    4. Pretrophozoite

    ANSWER: When a patient has diarrhea, the GI tract contents are moving through the system rapidly, thus there is no time for cyst formation. It is very likely the protozoan stage most likely to be seen will be the trophozoite. The term "pretrophozoite" is not a correct term. The correct answer is C.

  5. If amebic trophozoites measuring 14 µm, containing debris and a single nucleus with evenly arranged chromatin and a small, compact karyosome are seen in a permanent stained smear, they should be reported as:
    1. Entamoeba histolytica/E. dispar trophozoites
    2. Entamoeba hartmanni trophozoites
    3. Entamoeba dispar trophozoites
    4. Entamoeba histolytica trophozoites

    ANSWER: These trophozoites have morphologic characteristics that are consistent with Entamoeba histolytica/E. dispar. Without the specific presence of ingested RBCs in the cytoplasm or the use of specific immunoassay reagents, it will be impossible to identify these organisms as the pathogen, E. histolytica or the nonpathogen, E. dispar. The morphology of both trophozoites are basically identical (without the presence of ingested RBCs). The correct answer is A.

  6. The presence of Charcot-Leyden (C-L) crystals in the permanent stained smear indicates:
    1. Blood in the stool
    2. Excess yeast cells
    3. An immune response
    4. Nothing

    ANSWER: Charcot-Leyden crystals are formed from the breakdown products of eosinophils, thus the correct answer is (C). These crystals are an indication of an immune response, which may or may not be linked to a parasitic infection.

  7. A small lemon-shaped cyst is present in the permanent stained smear, and it has a single nucleus and a curved fibril that has been called "the shepherd's crook" - this organism is most likely:
    1. Pentatrichomonas hominis
    2. Enteromonas hominis
    3. Retortamonas intestinalis
    4. Chilomastix mesnili

    ANSWER: Chilomastix mesnili is a non-pathogenic flagellate that can be found in the feces. The description above accurately describes the cyst form of this organism (lemon-shaped, single nucleus, curved fibril called the shepherd's crook.. The correct answer is D.

  8. The presence of nonpathogenic protozoa in the intestinal tract indicates:
    1. The patient has ingested something contaminated with fecal material containing infective cysts
    2. The patient is likely to become symptomatic within a few days to two weeks
    3. The patient will remain asymptomatic for at least a month
    4. The patient also has pathogenic protozoa in the intestinal tract if additional stools are examined within 10 days

    ANSWER: The presence of nonpathogenic protozoa in the intestinal tract indicates the patient has ingested something contaminated with fecal material containing infective cysts. It does not necessarily mean pathogens are also present, nor does it mean the patient will become symptomatic. The correct answer is A.

  9. Intestinal protozoa that are considered nonpathogenic include:
    1. Blastocystis hominis and Entamoeba histolytica
    2. Endolimax nana and Entamoeba coli
    3. Giardia lamblia and Iodamoeba bütschlii
    4. Entamoeba hartmanni and Dientamoeba fragilis

    ANSWER: Nonpathogenic intestinal protozoa include Endolimax nana, Entamoeba coli, Iodamoeba bütschlii, and Entamoeba hartmanni. Pathogenic protozoa include: Blastocystis hominis, Entamoeba histolytica, Giardia lamblia, and Dientamoeba fragilis. Therefore, the correct answer is B.

  10. A protozoan cyst that contains four nuclei, median bodies and axonemes should be identified as:
    1. Giardia lamblia
    2. Trichomonas vaginalis
    3. Dientamoeba fragilis
    4. Pentatrichomonas hominis

    ANSWER: A protozoan cyst that contains four nuclei, median bodies, and axonemes can be identified as Giardia lamblia. None of the other intestinal flagellates mentioned have a cyst in the life cycle. The correct answer is A.

  11. Which of the following statements about Dientamoeba are correct?
    1. This organism is a flagellate with internal flagella
    2. Transmission is thought to occur through the ingestion of specific helminth eggs and the cyst form
    3. This organism is pathogenic and tends to be more commonly found in children
    4. All of the above.

    ANSWER: All of the responses contain correct information regarding the characteristics of Dientamoeba fragilis. Therefore, the correct answer is D, all of the above.

  12. Cryptosporidium parvum, Cyclospora cayetanensis, and Isospora belli are considered to be:
    1. Metazoa
    2. Microsporidia
    3. Sporozoa
    4. Coccidia

    ANSWER: The three organisms mentioned above are protozoa within the coccidia group. Therefore, the correct answer is D.

  13. Which of the following organisms are most likely to be seen in a direct wet mount from fresh stool?
    1. Entamoeba dispar cysts
    2. Blastocystis hominis trophozoites
    3. Entamoeba coli cysts
    4. Giardia lamblia trophozoites

    ANSWER: Protozoan cysts are not motile, therefore of the answers above, both (A) and (C) are eliminated. Blastocystis hominis does not move by pseudopods, flagella or cilia, so that answer is eliminated. Therefore, the correct answer is D; flagellate trophozoites move using their flagella for motility.

  14. Which of the following organisms are most likely to be recovered from duodenal aspirate material?
    1. Isospora belli and hookworm
    2. Giardia lamblia and Strongyloides stercoralis
    3. Cryptosporidium parvum and Enterobius vermicularis
    4. Microsporidia and Ascaris lumbricoides

    ANSWER: Of all the choices listed above, those organisms that might be recovered from the examination of duodenal aspirate would include: Giardia lamblia, Strongyloides stercoralis, Cryptosporidium parvum, and the microsporidia. Therefore, the correct answer is B.

  15. It is generally accepted that the most commonly recovered protozoan within the United States is:
    1. Entamoeba dispar
    2. Entamoeba coli
    3. Giardia lamblia
    4. Balantidium coli

    ANSWER: Of all the protozoa recovered from human fecal specimens, the most common is probably Blastocystis hominis; however, not all laboratories maintain statistics on this organism. So, the most common and most accurate response of those listed above would be Giardia lamblia. Therefore, the correct answer is C.

  16. Microsporidial spores are generally described as looking like:
    1. Coccidian oocysts
    2. Amebic cysts
    3. Fungal spores
    4. Bacteria

    ANSWER: Microsporidial spores in human intestinal infections generally measure approximately 1 to 2.5 microns, are oval, and tend to stain pink with the modified trichrome stains. This appearance tends to mimic bacteria or very small yeast. Therefore, the correct answer is D.

  17. In the human, microsporidian spores generally measure approximately:
    1. 1 to 4 µm
    2. 4 to6 µm
    3. 8 to10 µm
    4. None of the above

    ANSWER: Microsporidial spores in human infections (all body sites) generally measure approximately 1 to 4.0 microns. Therefore, the correct answer is A.

  18. The horizontal "stripe" or "bar" seen in microsporidial spores is actually the:
    1. Feeding groove fibril
    2. Polar tubule
    3. Vacuole outline
    4. Axostyle support rod

    ANSWER: The polar tubule is coiled within the microsporidial spore; evidence of this internal polar tubule is often seen in stained spores as a horizontal or diagonal "stripe" or "bar" that provides evidence that the object is a true microsporidial spore and not artifact. Therefore, the correct answer is B.

  19. Occasionally, structures can be seen within the Cryptosporidium parvum oocysts that are stained with the modified acid-fast stain; they are:
    1. Sporozoites
    2. Gametocytes
    3. Blastocysts
    4. Sporoblasts

    ANSWER: Cryptosporidium oocysts measure approximately 4 to 6 microns, are immediately infective when passed in the stool and contain four sporozoites. Although these sporozoites are not visible within every oocyst, the oocyst is still infective. Therefore, the correct answer is A.

  20. The following organisms are immediately infectious when passed in the stool (regardless of the stool consistency):
    1. Entamoeba histolytica cysts and Isospora belli oocysts
    2. Giardia lamblia trophozoites and Cyclospora cayetanensis oocysts
    3. Microsporidian spores and Endolimax nana trophozoites
    4. Cryptosporidium parvum oocysts and Entamoeba coli cysts

    ANSWER: Although protozoan cysts are generally infectious when passed, trophozoites are not. Neither Isospora or Cyclospora oocysts are infective when passed. Therefore, the correct answer is D.

  21. Which of the following infections are more likely to cause major symptoms in the immunocompromised patient?
    1. Entamoeba dispar
    2. Enterocytozoon bieneusi
    3. Pentatrichomonas hominis
    4. Giardia lamblia

    ANSWER: It has been well documented that microsporidial infections (Enterocytozoon bieneusi) in the compromised host can cause major symptoms/disease. Both Entamoeba dispar and Pentatrichomonas hominis are nonpathogenic, and, although Giardia lamblia is pathogenic, the infection in the compromised host may not be that different from that seen in the immunocompetent host. Therefore, the correct answer is B.

  22. Which of the following should be quantitated (rare, few, moderate, many, packed) on the laboratory report form?
    1. White blood cells (WBCs) and Blastocystis hominis
    2. Red blood cells (RBCs) and Entamoeba histolytica
    3. Budding yeast cells and Giardia lamblia
    4. Charcot-Leyden crystals and microsporidian spores

    ANSWER: Generally, it is not recommended that intestinal protozoa be quantitated on the report form; however, there is one exception and that is Blastocystis hominis. There may be a relationship between numbers and symptoms, so the recommendation is to report and quantitate this particular organism. It is also recommended that WBCs, RBCs, and budding yeast cells should be quantitated when reported. Therefore, the correct answer is A.

  23. If Entamoeba spp. trophozoites are seen in a permanent stained smear (no ingested RBCs, 13 µm, nucleus with evenly arranged chromatin and small, compact karyosome), they should be reported as:
    1. Entamoeba histolytica trophozoites
    2. Entamoeba coli trophozoites
    3. Entamoeba dispar trophozoites
    4. Entamoeba histolytica/E. dispar trophozoites

    ANSWER: If Entamoeba spp. trophozoites with the above characteristics are seen in the permanent stained smear, the correct identification should be Entamoeba histolytica/E. dispar trophozoites. Unless RBCs were seen in the cytoplasm of the trophozoite, one could not identify the organism as a true pathogen, Entamoeba histolytica. Entamoeba coli would tend to have uneven nuclear chromatin with a large, eccentric karyosome. The correct answer is D.

  24. Balantidium coli trophozoites and cysts are best seen in the:
    1. Permanent stained smear
    2. Direct wet preparation
    3. Concentration wet preparation
    4. Agar plate culture

    ANSWER: Because Balantidium coli trophozoites and cysts are so large, they tend to overstain on the permanent stained smear and can be confused with helminth eggs and/or artifacts. The best approach to identification is the examination of the concentration wet preparation, where the morphology (including cilia on the trophozoite) can be easily seen. Therefore, the correct answer is C.

  25. All but which one of the following organisms tends to cause a severe watery diarrhea, particularly in the compromised patient?
    1. Cryptosporidium parvum
    2. Enterocytozoon bieneusi
    3. Balantidium coli
    4. Trichomonas vaginalis

    ANSWER: Trichomonas vaginalis is a pathogenic flagellate that can be found in the urinary-genital tract; it is not found in the stool and does not cause diarrhea. The correct answer is D.

  26. In a patient with diarrhea, occasionally Entamoeba histolytica/E. dispar four nucleated cysts (no chromatoidal bars) are identified as being present; however, these cells that have been misdiagnosed as protozoa are really
    1. Macrophages
    2. Polymorphonuclear leukocytes
    3. Epithelial cells
    4. Eosinophils

    ANSWER: When a patient has diarrhea, the intestinal contents move through the system very quickly; consequently, there is no time for protozoan cyst formation. When polymorphonuclear leukocytes (PMNs) are in the stool for some time, the lobed nuclei come apart and can resemble protozoan cysts with four separate "nuclei" - however, these "protozoan cysts" are really human cells. Therefore, the correct answer is B.

  27. Charcot-Leyden crystals in human clinical material are frequently associated with an immune response and are thought to be the breakdown products of
    1. Neutrophils
    2. Eosinophils
    3. Monocytes
    4. Lymphocytes

    ANSWER: Charcot-Leyden (CL) crystals are formed from the breakdown products of eosinophils. Therefore, the correct answer is B.

  28. Parasitic organisms that may be sexually transmitted include
    1. Pentatrichomonas hominis
    2. Dientamoeba fragilis
    3. Trichomonas vaginalis
    4. Enteromonas hominis

    ANSWER: Trichomonas vaginalis is known to cause a sexually transmitted disease, trichomoniasis. The other organisms are found in the intestinal tract. Therefore, the correct answer is C.

  29. The specimen that is LEAST LIKELY to provide recovery of Trichomonas vaginalis is
    1. Urine
    2. Urethral discharge
    3. Prostatic discharge
    4. Feces

    ANSWER: Trichomonas vaginalis is found in the urinary-genital tract and does not inhabit the intestinal tract. Therefore, the specimen that is least likely to provide recovery of this organism is the stool specimen. The correct answer is D.

  30. The recommended technique for the recovery of Dientamoeba fragilis from stool is the
    1. Formalin concentrate
    2. Trichrome stained smear
    3. Modified acid-fast stained smear
    4. Giemsa stain

    ANSWER: Dientamoeba fragilis is a pathogenic flagellate that now has a confirmed cyst form in the life cycle. However, the number of cyst forms on a patient smear is only about 1% and they are very difficult to identify.  Therefore, the most important method for the identification of this organism remains the permanent stained smear (trichrome, iron-hematoxylin, etc.); without using this approach, the majority of infections using wet mount examination only will be missed. Therefore, the correct answer is B.

HOPE YOU HAVE ENJOYED THE QUIZ!

 

REFERENCES

  1. Garcia, L.S. 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, D.C.
  2. Leber, A.L. and S.M. Novak. 2003. Intestinal and Urogenital Amebae, Flagellates, and Ciliates In: Murray, P.R., E.J. Baron, J.H. Jorgensen, M.A. Pfaller, and R.H. Yolken (eds). Manual of Clinical Microbiology, 8th ed, vol 2, ASM Press, Washington, D.C.